The two Collie mines supply coal to plants run by privately-owned Bluewaters and State-backed Synergy that collectively represent almost all WA coal-fired power production.

Dr Nahan has said coal will continue to be vital to power production in the South West because it is by far the most affordable source.

Shadow energy minister Bill Johnston said last year's increase in coal-fired generation could be explained by the reintroduction of Muja AB, the 60-year-old power plant controversially refurbished by the Government.

Mr Johnston said though coal had become more affordable in light of higher gas prices, its price, too, was set to rise.